The present invention relates to a process for the transalkylation of aromatics, particularly the transalkylation of polyisopropylbenzene (PIPB) with benzene to produce cumene and the transalkylation of polyethylbenzene (PEB) with benzene to produce ethylbenzene. Ethylbenzene is a valuable commodity chemical and is used in the production of styrene monomer. Cumene (isopropylbenzene) is also a valuable commodity chemical and is used in the production of phenol and acetone.
Presently, ethylbenzene is often produced by a liquid phase alkylation process from benzene and ethylene in the presence of an alkylation catalyst. The liquid phase process operates at a lower temperature than its vapor phase counterpart. One advantage of the liquid phase alkylation is a lower yield of undesired by-products, polyalkylated aromatic compound(s). The alkylation of aromatic hydrocarbon compounds employing zeolite catalysts is known and understood in the art. U.S. Pat. No. 5,334,795 describes the liquid phase alkylation of benzene with ethylene in the presence of MCM-22 to produce ethylbenzene; and U.S. Pat. No. 4,891,458 discloses liquid phase alkylation and transalkylation processes using zeolite beta.
Zeolite-based catalysts are used in the alkylation of benzene with propylene to produce cumene. U.S. Pat. No. 4,992,606 discloses a process for preparing cumene using MCM-22 in liquid phase.
Commercial alkylation processes for the production of ethylbenzene and cumene typically produce certain polyalkylated by-products in addition to ethylbenzene and cumene. The polyalkylated aromatic compound(s) may be transalkylated with benzene or other alkylatable aromatic compound(s) to produce ethylbenzene or cumene. This transalkylation reaction may be accomplished by feeding the polyalkylated aromatic compound(s) through a transalkylation reactor operated under suitable conditions and in the presence of a transalkylation catalyst. Also, the polyalkylated aromatic compound(s) may be recycled to an alkylation reactor in the presence of an alkylation catalyst that is capable of performing the transalkylation reaction. The polyalkylated aromatic compound(s) typically include bi-alkylated benzenes (e.g., bi-ethylbenzene(s) or bi-isopropylbenzenes) and tri-alkylated benzene(s) (e.g., tri-ethylbenzenes or tri-isopropylbenzenes). Commercial transalkylation catalysts typically have bi-alkylated benzenes conversion of about 50 wt. % to 90 wt. %, but low tri-alkylated benzenes conversion (e.g., less than 20 wt. %) under the same conditions. U.S. Pat. No. 5,557,024 discloses a process for preparing short chain alkyl aromatic compounds using MCM-56 and the use of zeolite catalysts such as MCM-22, zeolite X, zeolite Y and zeolite beta for the transalkylation of the polyalkylated aromatic compound(s).
However, none of these references contemplate a transalkylation process with a transalkylation catalyst which is maintained under conditions sufficient to yield a ratio of bi-alkylated aromatic compound(s) conversion over tri-alkylated aromatic compound(s) conversion in a range of from about 0.5 to about 2.5 at a temperature less than 300° C.